Field of the Invention
The present invention relates to a spectroscopic measurement apparatus.
Related Background Art
In an infrared range, in particular, a region having a wavelength of 2.5 to 25 μm is referred to as a fingerprint region, and an absorption peak specific to a substance appears in the region, therefore, the region is used to identify the substance. When absorption characteristics of the substance in the infrared range are measured, Fourier transform infrared spectroscopy (FTIR) technique is mainly used.
In the FTIR, a measurement sample is arranged on one optical path of two optical paths in an interference optical system, and an optical path length difference between the two optical paths is scanned so that interference intensity data is obtained in time series, and by performing Fourier transform to the time series data, absorption information on the measurement sample in each wavelength is obtained. For this reason, the FTIR needs a huge amount of time series data to obtain detailed information on the measurement sample. However, due to the property of a laser light source used as a light source, the number of data obtained per unit time is limited. Since it is necessary to perform measurement for a long time in order to increase the number of data, it is difficult to perform high-speed measurement.
On the other hand, a dispersion type spectroscopic measurement apparatus has been known other than the FTIR. The dispersion spectroscopic measurement apparatus detects the intensity of the light in each wavelength by a detector by spatially dispersing the light which has passed through the measurement sample by a spectroscopic unit and propagating the light to different optical paths according to the wavelength, and then, the apparatus obtains the absorption information on the measurement sample in each wavelength. The intensities of the light components in a plurality of wavelengths can be simultaneously detected by using a plurality of detectors, and therefore, high-speed measurement can be performed. However, it is necessary to use the detector corresponding to each wavelength. Since it is necessary to use many detectors to obtain the detailed absorption information on the measurement sample, the apparatus gets to be expensive.
An apparatus disclosed in Patent Document 1 is for measuring a cholesterol concentration, and by using a plurality of bandpass filters having different transmission wavelength bands from each other as sequentially switching them, absorption information on the measurement sample (cholesterol) in each wavelength is obtained, and the cholesterol concentration is measured. However, since it is necessary to sequentially switch many bandpass filters, it is difficult to perform high-speed measurement.
An apparatus disclosed in Patent Document 2 is for identifying a tooth color based on spectroscopic characteristics of teeth, and by using a filter having loss characteristics according to the spectroscopic characteristics in the measurement sample (teeth), the color of the measurement sample (tooth) is classified from light intensity measurement data measured a few times. However, it is difficult to product the filter according to the measurement sample, and also, there is a possibility that the apparatus becomes expensive.
An apparatus disclosed in Patent Document 3 is for measuring an amount of atmospheric gas, and by combining an etalon, a bandpass filter, and a spatial dispersion by a diffraction grating, a change in an absorbance in an absorption wavelength of the measurement sample (atmospheric gas) is compared with the intensity of the wavelength (window band) which is not absorbed by the measurement sample, and then, the apparatus constantly monitors the atmospheric gas amount.
The apparatus disclosed in Patent Document 3 measures the absorbance in a specific single absorption wavelength of the measurement sample. In the evaluation of the kind of a part of the atmospheric gas, only when it is not necessary to consider another substance having absorption in the same band, the amount can be evaluated by measuring the absorbance in a single wavelength. However, when the absorption wavelength of the measurement sample is similar to or same as the absorption wavelength of another sample, the samples cannot be distinguished (identified).                Patent Document 1: Japanese Patent Publication No. 5591680        Patent Document 2: Japanese Patent Publication No. 4508476        Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2001-108613        